Show that `f(x)=cos(2x+pi/4)`is an increasing function on `(3pi//8,7pi

1.	Show that `f(x)=cos(2x+pi/4)`is an increasing function on `(3pi//8,7pi//8)dot`
Answer» given that `y= f(x)= cos(2x+pi/4)` `dy/dx> 0 => -2sin(2x+pi/4)> 0` `2sin(2x+ pi/4) <0` `sinubrace(2x+ pi/4) < 0 ` `sin a < 0`so, `pi< a<2pi` so must satisfy `pi< 2x+pi/4<2pi` `(3pi)/4 < 2x < (7pi)/4` `(3pi)/8 < x < (7 pi)/8` answer

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